• around 30 s, when the loader is raised and the bucket slightly rotated, but the contemporaneity of the movement
of the actuators happens for a very reduced time interval: in this phase the system requires medium-high flow and pressure is high to raise the load. The traditional single spool distributor works with the outlet section partially closed, because it’s linked to the partial opening of the inlet section. The independent metering valve leaves the outlet section fully open and operate flow control on the meter-in section. The direct control of pump displacement is slightly more efficient because it saves the pump pressure margin that is used in the load sensing systems and hence meter in losses are very low.
• around 35 s, when the bucket rotates before unloading: in this phase a small load acts on the bucket cylinder,
pressure is in a low range and difference within the three systems behaviours is not very high. Again, direct pump displacement control saves the energy that is necessary to generate the pump pressure margin in the load sensing systems.
• 38-40 s, when the bucket unloads: first the user asks for high flow to rotate the bucket and unload then gravity
drags the bucket and the load becomes overrunning for a brief time interval. Here energy saving is debatable: it depends strictly on the overrunning margin used to recognize an overrunning load by monitoring the pressures in the two actuator chambers. In the independent metering architectures when an overrunning condition is detected, the control strategy induces a pressure control on the meter in section and a flow control on the meter out section. Thus may be in contrast with energy saving but provides good control over the actuators. Traditional distributors are designed to maintain control only in cases of limited overrunning loads but they may lose control when unexpected high overrunning loads are involved in the duty cycle. A more efficient management of overrunning load offers minor energy savings and avoids cavitation. When the load becomes passive again, the independent metering architectures are more efficient.
• 41- 44 s, the loader is finally lowered, an overrunning load condition is recognized by the alternative
architectures at the beginning of the operation, which changes into a passive load condition after a short time: here more efficient management of both situations leads to consistent energy savings in the independent metering architectures compared to traditional systems.